Fibrillin expression is regulated by abscisic acid response regulators and is involved in abscisic acid-mediated photoprotection

Abstract

Fibrillins are lipid-binding proteins of plastids that are induced under abiotic stress conditions. In response to environmental stress, plants generate abscisic acid (ABA) as an endogenous signal. We show that ABA treatment and fibrillin accumulation enhance the tolerance of photosystem II toward light stress-triggered photoinhibition in Arabidopsis. ABA induces fibrillin accumulation, and the ABA response regulators ABI1 and ABI2 regulate fibrillin expression. The abundance of fibrillin transcripts was specifically reduced in the ABA-insensitive abi1 mutant but not in the abi2 mutant. However, leaves of abi2 revealed in comparison to WT and abi1 enhanced fibrillin levels, pointing to a posttranscriptional control mechanism. Protein interaction analysis identified the protein phosphatase ABI2 to target the preprotein of fibrillin. Interaction was abrogated either by deleting the signal peptide of prefibrillin or by the single amino acid exchange present in the phosphatase-deficient abi2 protein. Thus, ABI1 and ABI2 seem to control fibrillin expression that is involved in mediating ABAinduced photoprotection.ABI1 ͉ ABI2 ͉ abiotic stress ͉ photoinhibition ͉ light stress F ibrillins are plastid-associated lipid-binding proteins that are ubiquitous in plants (1, 2). They have been primarily characterized from chromoplasts of tomato and pepper fruits and are known to accumulate during abiotic stress in plastids e.g., inflicted by high light, cold, and drought (3-5), and also during pathogen infection (6). The family of fibrillin-like proteins is unique to plants, and the members contain a hydrophobic domain that associates with or anchors within lipids (7). Fibrillins associate with stromal lamellae of thylakoids and fibrillic carotenoid-containing structures of chromoplasts (3,8). A model for the fibrillic structures predicts a layer of fibrillin shielding polar lipids and carotenoids (1). In potato, the fibrillin C40.4 protein is specifically associated with the photosystem II (PSII) light-harvesting complex with a presumptive role in the modulation of photosynthetic efficiency (9). A posttranslational control of fibrillin accumulation by abscisic acid (ABA) was indicated by studies on ABA-deficient tomato that failed to accumulate fibrillin despite normal transcript levels (5). Although fibrillin is induced in response to abiotic stress, its role in stress responses and the molecular mechanism regulating its accumulation are still elusive.ABA plays a major role in regulating plant growth and development and mediating adaptations to environmental stress such as cold, drought, and salinity (10). ABA regulates ion channel activities involved in osmoregulation and stomatal closure and influences gene expression at the transcriptional and posttranscriptional levels (11,12). Key regulators of diverse ABA-mediated responses are ABI1 and ABI2. Both proteins are members of a larger family of plant protein phosphatases 2C (PP2Cs), several of which act negatively in a partially redundant manner on ABA responses (13-15). The...

Fibrillin 5 Is Essential for Plastoquinone-9 Biosynthesis by Binding to Solanesyl Diphosphate Synthases in Arabidopsis

“…FBN5 is a phylogenetically distant relative of other fibrillins in Arabidopsis (Singh and McNellis, 2011), and it localizes to the stroma, with a lower pI and lower hydrophobicity than the other fibrillins (Lundquist et al, 2012). Therefore, FBN5 may play different roles from those previously reported for the fibrillins that localize primarily to the plastoglobules (Trebst, 1978;Yang et al, 2006;Singh et al, 2010Singh et al, , 2012Youssef et al, 2010). Surprisingly, we found that FBN5 specifically interacts with two solanesyl diphosphate synthases, SPS1 and SPS2, in the chloroplasts.…”

“…Recently, fibrillin mutants of Arabidopsis have extended our understanding of the functions of the fibrillin proteins. The Arabidopsis FIBRILLIN1 (FBN1) gene family is involved in abscisic acid-mediated protection from photoinhibition (Yang et al, 2006), and the FBN1 and FBN2 gene families modulate jasmonate biosynthesis during light and cold stress (Youssef et al, 2010).…”

The Nuclear Interactor PYL8/RCAR3 ofFagus sylvaticaFsPP2C1 Is a Positive Regulator of Abscisic Acid Signaling in Seeds and Stress

“…Interestingly, the interaction between FsPP2C1 and PYL7/RCAR2 and PYL5/RCAR8 is also present mostly in the nucleus. It is noteworthy that most of the targets previously identified for clade A PP2Cs were not nuclear proteins (Cherel et al, 2002;Guo et al, 2002;Ohta et al, 2003;Miao et al, 2006;Yang et al, 2006;Yoshida et al, 2006a). However, it is supposed that the interaction of ABI1 with the transcription factor ATHB6 must be nuclear (Himmelbach et al, 2002).…”

Abscisic acid sensor RCAR7/PYL13, specific regulator of protein phosphatase coreceptors

“…Values are means ± SDs of four replicates. Yeast two-hybrid tests were carried out for analysis of receptorcoreceptor interaction as described (3). HAB1 (AT1G72770), HAB2 (AT1G17550), PP2CA (AT3G11410), HAI1 (AT5G59220), HAI2 (AT1G07430), HAI3 (AT2G29380), AHG3 (AT3G11410), and PP2CE (AT5G27930) were amplified from a cDNA library as mentioned (8), cloned into the pGAD vector (Clontech), and expressed as activation domain fusion proteins.…”

“…ABA accumulates in response to water deficit and triggers rapid physiological responses for homeostasis of plants' water status. The immediate response includes stomatal closure to limit transpiration and initiation of adaptive gene expression (1,2), including protection of the photosynthetic machinery (3). ABA perception occurs by soluble ABA receptors acting in concert with protein phosphatases 2C (PP2Cs) of clade A (1,(4)(5)(6).…”